1. Field of the Invention
The present invention relates to a renewable energy source for building structures and more particularly to building structures that are configured to take advantage of differences of the temperatures of air in a vertical air column and the ambient air to generate electricity based upon the so-called stack effect.
2. Description of the Prior Art
The stack effect is well known and relates to a natural updraft that is created based upon a difference in temperatures between air masses at different elevations. In industrial applications, the byproducts of industrial processes performed in furnaces result in flue gases at relatively high temperatures. These flue gases are known to be vented to the atmosphere by way of a stack. A stack is a relatively tall hollow vertical structure which is open to the atmosphere on an upper end and receives the flue gases on an lower end.
The flue gases can be 1000° F. or more while the temperature of the atmosphere can vary, for example, between −25° F. and 105° F. depending on the location. In such an application, the hot flue gases will be less dense the ambient air. As such, the flue gases will flow naturally toward the atmosphere creating a natural updraft or pressure difference between the bottom of the stack and the top of the stack. The magnitude of the pressure difference is a function of the temperature difference between flue gases and the ambient temperature.
The stack effect is also found in residential structures. For example, many residential structures are known to have supplemental heating units, such as fireplaces and wood burning stoves, which supplement the heat supplied by forced air gas furnaces. These supplemental heating units include a fire box for burning wood or other combustibles and a chimney or stack for venting flue gases resulting from the combustion process to the atmosphere. Since the temperature in the fire box of the supplemental heating unit will always be hotter than the outside ambient temperature when wood is burned in the fire box, a stack effect will be created and the flue gases from the combustion process will be vented to the outside ambient air.
Recent attempts have been made to harness the energy created by the stack effect in order to create a renewable energy source. For example, French Patent Publication No. FR2956427 A1 discloses a “solar chimney”. The solar chimney includes a stack this is juxtaposed from the ground level to the top of a high rise building. The solar chimney also includes a “collector” and a wind generator. Two embodiments of the solar chimney are disclosed. In one embodiment, the stack is located outside the building and attached to a façade, In this embodiment, the solar chimney appears to have a metal frame attached to one façade of a high rise building that is covered by a polyester material covered on both sides with polyvinyl chloride. In the alternative embodiment, the solar chimney is located inside the building. In both embodiments, a wind generator is located at the base of the solar chimney for converting wind energy created by the stack effect to electricity. A solar collector, formed as a greenhouse is formed with a diameter of 3-4 kilometers surrounds the solar chimney. The greenhouse is formed at the base of the building with a transparent roof for collecting solar, i.e. heat energy from the sun. As such, the air temperature in the greenhouse will generally be much hotter than the ambient air temperature adjacent the solar chimney on the roof, This difference in temperature will result in a stack effect and cause the hotter air in the greenhouse to rise to the top of the solar chimney. This action, in turn, will cause the blades of the wind generator to spin and generate electricity.
The greenhouse is formed as part of the vestibule of the building and is open to pedestrian traffic. As such, any pedestrians in the greenhouse will be fairly uncomfortable due to the high temperature caused by the greenhouse effect in the greenhouse.
U.S. Pat. No. 4,122,675 discloses a system for a high rise building for implementing the stack effect in order to generate electricity by way of wind generators. In particular air ducts are provided on opposing sides of the building. These air ducts extend from a location spaced above the base of the building and converge at the top of the building in a manifold. A wind generator is located in the manifold, strategically located to receive the air drafts created by the stack effect from both air ducts. Outwardly projecting air inlets in fluid communication with the air ducts are provided at spaced apart vertical locations from the bottom of the air ducts to just below the manifold where the air ducts converge. An air plenum located above the wind generator is provided with opposing horizontal openings for exhausting the air from the air ducts. Such a configuration is used to potentially take advantage of ambient wind currents adjacent the top of the building that can potentially lower the pressure in the air plenum in order to increase the speed of the air flow from ducts and consequently increase the electricity generated by the wind generators.
The configuration of the building disclosed in the '675 patent is not well suited for taking advantage of the stack effect. In particular, the ambient air temperature at the various vertical air intakes may not vary sufficiently to cause a stack effect. However, the structure disclosed in the '675 patent is configured to take advantage of ambient winds in order to cause the blades of the wind generator to rotate.
U.S. Pat. No. 7,757,490 discloses a bio-tower which includes a vertical air duct or chimney extending from ground level to the top of the tower. A lower level glass roof surrounds the bio-tower and provides a covered area for various purposed. An ambient air intake is provided to be in fluid communication with the chimney and is located just below the glass roof. In addition, waste heat from adjacent buildings is channeled so as to be in fluid communication with the chimney. The ambient air intake is provided with a controllable air inlet device, such as a damper or louver, in order to close the air intake when the waste heat is being supplied from the air conditioning units in adjacent buildings. A wind generator is disposed to be in fluid communication with the chimney. An air outlet is provided on top of the chimney.
As stated in the '490 patent, air flow in the chimney is driven by the waste heat from air conditioning systems. The ambient air intake is for capturing wind to further augment the stack effect created by the waste heat from the air conditioning systems from adjacent buildings.
The system disclosed in the '490 patent has several drawbacks. One drawback is the cost of providing the waste heat from adjacent buildings to take advantage of the stack effect. Such an undertaking would be relatively expensive. Additionally, the building implementing the system disclosed in the '490 patent would not be self-contained and would be dependent on the operation of the air conditioning systems in adjacent buildings. The system disclosed in the '490 patent could only likely be implemented if all of the buildings involved are commonly owned and built at the same time.
Thus, there is a need for a renewable energy system that takes advantage of the stack effect to generate electricity that does not suffer from the problems identified with the prior art.